Thermal and Light-Induced Spin Crossover Phenomena in New 3D Hofmann-Like Microporous Metalorganic Frameworks Produced As Bulk Materials and Nanopatterned Thin Films

Abstract

Three novel three-dimensional coordination polymers, {FeII(azpy)[(MII(CN)4)]}·nH2O (azpy = 4,4′-azopyridine; M = Ni, Pd, and Pt), have been synthesized as polycrystalline bulk materials and as continuous as well as nanopatterned thin films on gold substrates. Single crystals of the Pt derivative have also been isolated and the corresponding X-ray diffraction analysis at 140 K indicates that it crystallizes in the tetragonal P4/mmm space group with a = b = 7.1670(5) Å, c = 13.0330(13) Å, V = 669.40(9) Å3 and Z = 1. Four square-planar [Pt(CN)4]2− anions occupy the equatorial positions of [FeIIN6] octahedron and four Fe(II) atoms are coordinated to each [Pt(CN)4]2− anion, thereby defining an infinite set of 2D planar layers pillared by the azpy ligands which bridge through the axial positions consecutive Fe(II) atoms. Magnetic susceptibility, calorimetric, and Mössbauer measurements reveal the occurrence of a thermal spin crossover phenomenon in the powder samples, which depends strongly on the water-content of the lattice in the case of Pd and Pt derivatives. The spin crossover is less cooperative with T c = 245 K in the case of Ni, but the Pd (Pt) analogues display almost complete spin transitions with a hysteresis loop centered around 292 (280) and 191 (183) K, in the hydrated and dehydrated forms, respectively. Thin films of the three compounds were grown via a sequential assembly method using coordination reactions. Raman spectroscopic study proves that thermal spin crossover, similar to the bulk forms, occurs in the films. With the exception of the bulk Ni complex, a virtually complete light-induced spin conversion (LIESST effect) is detected by Raman spectroscopy in the thin films as well as in the powders below ca. 130 K.

Photothermal studies of the room temperature photo-induced spin state change in the Fe(III)(salten)(mepepy) complex

“…More recently, thermal and photo-induced spin crossover in novel 3D metal organic materials was examined in both bulk materials and thin films. These studies also revealed very small enthalpy changes ranging from $1 to $4 kcal mol À1 at temperatures below 300 K [8].…”

Tuning the Spin States of Two Apical Iron(II) Ions in a Pentanuclear Iron(II) Cluster Helicate through the Choice of Anions

“…Firstly, among the three compounds, hydrogen bond interactions exist between the {Fe 5 } cation cluster and the anion cluster. Different acceptor atoms of the hydrogen bonds and differences in the hydrogen bonds would probably influence the electronic configuration in the metal center, thus affecting the magnetic behavior [45,46] (see in Tables S1-S3). In addition, the π-π stacking effect between neighboring ion clusters is observed in both 1 and 2, and the π-π effect in 2 is obviously stronger than in 1.…”

Crystallography of Representative MOFs Based on Pillared Cyanonickelate (PICNIC) Architecture

“…These compounds undergo cooperative spin transitions at high temperatures, and the host-guest interactions inside the pores have considerable effects on the spin crossover properties of these materials. Agusti et al [60] observed the thermal and light-induced spin crossover phenomena in the 3-D MOF of {[Fe II (azpy)[M II (CN) 4 ]}·nH 2 O (azpy = 4,4'azopyridine; M = Ni,Pd and Pt).…”

“…These compounds undergo cooperative spin transitions at high temperatures, and the host-guest interactions inside the pores have considerable effects on the spin crossover properties of these materials. Agusti et al [60] In recent years, National Energy and Technology Laboratory (NETL) has been one of the leading laboratories in the area of science and engineering research of novel Ni(CN)4-based flexible MOFs [56,[61][62][63][64][65]. The precursors of these flexible MOFs are typically a cyanometallate complex that acts as a ligand and a transition metal complex with available coordination sites.…”